In previous work by this investigator, the glucocorticoid dexamethasone (dex) was found to inhibit the activity of the hexose transport system and of three amino acid transport agencies of the plasma membrane of rat hepatoma (HTC) cells in suspension tissue culture. The inhibitory effect of dex was partially counteracted by insulin in the case of hexose transport and in one of the amino acid transport systems. The objectives of this project are twofold: (A) to determine whether the membrane transport inhibitory effect of dex and its counteraction by insulin are also a characteristic of isolated hepatocytes; and (B) to determine whether glucocorticoids and possibly insulin affect the membrane processes in HTC cells by changing membrane lipids. HTC cells originated from malignant transformation of liver cells and have retained some liver-specific functions. Hence the possibility exists that similar plasma membrane changes could be elicited by glucocorticoids and insulin in the liver. Such hormonal effects on the hepatocyte plasma membrane would: (1) explain the deleterious effects of glucocorticoids on the tolerance to oral glucose loads; (2) indicate that the plasma membrane transport of glucose could modulate the rates of utilization of this sugar by the liver; and (3) indicate that insulin can modify membrane transport of glucose in the hepatocyte, a function not previously considered to be a target for insulin action. The simplest alteration that could explain the multiple transport effects observed in HTC cells is a change in membrane lipids. Both glucocorticoids and insulin are known to produce changes in the lipids of membranes from other cell types. It is well known that rates of transport are affected by changes in the lipid composition of the membranes. Yet, to present no physiologic modulator of transport such as hormones, have been shown to alter transport via alterations of membrane lipids. We will investigate this hypothesis by studying the effects of dex and insulin on HTC cell plasma membrane lipid composition and by reproducing any observed hormonal alteration of the lipids by means other than the hormonal treatment and subsequently observe the effects on transport.